Apparatus for adjusting the backlash on a differential

ABSTRACT

An apparatus for adjusting the backlash on a differential has a clamp for holding the pinion gears to the housing, locating means for precisely positioning the housing and bevel gear relative to one another, an air cylinder to press the bevel gears towards the pinion gear, and a micrometer used to measure the travel distance of the bevel gear. The clamp preferably also includes tangs resiliently pressing the bevel gear away from the pinion gears, both to aid in separating the bevel gear from the pinion gears and to compress any clutch pack in the differential, e.g., if it is a limited slip differential.

This application is a division of U.S. Pat. No. 4,821,395 applicationSer. No. 07/172,153, filed 23 Mar. 1988.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to techniques for adjusting the backlashbetween the bevel gears and the pinion gears in a bevel-typedifferential.

2. Description of the Related Art

A typical bevel-type differential has two bevel gears and a plurality ofpinion gears, typically four, mounted in a differential housing. If itis a limited slip differential, various clutch and separator plates alsoare provided between each bevel gear and the housing to clutch the twotogether. For proper operation, a small amount of play or backlashnormally is provided between each bevel gear and the pinion gears. Theamount of play typically is adujsted by changing the thickness of a shimbetween the bevel gear and the housing, or, in the case of the limitedslip differential, between the clutch pack and either the housing or thebevel gear.

Due to manufacturing tolerances, the backlash between each bevel gearand the pinion gears normally must be adjusted for each differential byadjusting the thickness of the shim used. In the past, this has beenaccomplished by placing one of the bevel gears and the clutch pack (ifany) in the corresponding half of the differential housing. The piniongears on the shaft then are placed on top of the housing in the positionthey will occupy upon final assembly. The pinion gears are then movedback and forth by hand, and a micrometer is used to measure the backlashdirectly, i.e., to measure how far each pinion gear moves before itengages the bevel gear. The average measured backlash of all the piniongears is then used to estimate the shim pack thickness required to bringthe backlash within design specifications. A shim pack of this size thenis added and the process repeated until the appropriate backlash isobtained. The entire process then is repeated with the other bevel gearin the other half of the differential housing. The adjustment andassembly process for the complete differential can take as much as threehours.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide atechnique and apparatus for significantly reducing the amount of timerequired to adjust and assemble a differential.

According to the present invention, instead of moving the pinion gearsback and forth to determine the backlash, the pinion gears are heldagainst the differential housing and the bevel gear is moved upwardstowards the pinion gears. It is a relatively simple matter to calculateahead of time how far the bevel gear should move towards the piniongears when the spacing therebetween is at the appropriate backlash. Thiscorrect distance is subtracted from the measured actual travel distancefrom the bevel gear to provide the appropriate shim thickness. Such ashim then is added to the differential, the displacement is verified,and adjustment for that bevel gear is complete. The process is repeatedfor the other bevel gear, and the differential then is assembled. Usingthe apparatus discussed below, the entire process can be accomplished injust ten minutes.

The apparatus according to the present invention for carrying out themethod just described has a locating ring on which a differentialhousing half can be positioned in a predetermined location. The bevelgear, clutch pack (if any) and pinion gears are placed in thedifferential housing, and the mechanism clamps the pinion gear shaftsdown to the housing. The mechanism also preferably presses the bevelgear and clutch pack together to eliminate any play therebetween, whichwould result in a false reading. An air cylinder is provided to pressthe bevel gear up against the pinion gears. While manual pressure couldbe provided, the air cylinder eliminates variances due to varyingoperator force in a manual situation. A micrometer provided on theapparatus measures the displacement of the air cylinder and the bevelgear. If desired, the micrometer could be labeled to indicate directlythe thickness of the appropriate shim, possibly with several differentscales depending on the differential being adjusted. After measurementis made, the clamp is released and the differential is partiallydisassembled to allow addition of the shim pack. It then is reassembled,reclamped and the measurement verified. The entire process is repeatedwith the other half of the differential housing, and the differential isassembled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view in partial section of the apparatus according to thepresent invention.

FIG. 2 is a plan view along the line 2--2 in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The figures depict a preferred apparatus according to the presentinvention for carrying out the method according to the presentinvention. As shown in FIG. 1, the apparatus has a clamp 10, an aircylinder 12, and a micrometer 14 mounted to a base 16. A locating ring18 also is mounted to the base 16 coaxially with the air cylinder 12. Inuse, the bearing extension 20 of the differential housing half 22 fitssnuggly inside the inner rim 24 of the locating ring 18, therebyprecisely positioning the differential housing half 22 relative to theair cylinder 12.

The apparatus is illustrated with half of a limited slip differential 13mounted thereon. In addition to the differential housing half 22, thedifferential includes a plurality of interleaved clutch plates andseparators forming a clutch pack 26, a bevel gear 28, and a plurality ofpinion gears 30 mounted on corresponding cross pins 32. The cross pins32 rest in suitable depressions 34 formed in the differential housing22. A shim 36 also is provided between the clutch pack 26 and thedifferential housing half 22.

The clamp 10 serves to clamp the cross pins 32 into the depression 34and to fully compress the clutch pack 26 and bevel gear 28. Inparticular, the clamp 10 has a clamp cup 38 at one end thereof, theouter rim of which presses down against the cross pins 32 when the clampis closed, thereby forcing the cross pins 32 firmly into the depressions34. The cup is shaped to avoid interferring with movement of the piniongears 30, which therefore remain free to rotate around their respectivecross pins 32. The clamp also is provided with a plurality of fingers ortangs 40 extending down from the center thereof to press against theupper surface of the bevel gear 28, thereby compressing the clutch pack26 and bevel gear 28. These tangs 40 extend from a central cylinder 42which is slidably mounted on the cup 38 by a shoulder screw 44. A spring46 extending between the cup 38 and the tangs 40 biases the tangs 40towards the bevel gear 28. As shown in FIG. 2, the tangs 40 are sizedand positioned to extend between the cross shafts 32 without interferingwith them or with the bevel gears 30. Returning to FIG. 1, clampingforce is provided for the clamp 10 by a simple over-center mechanism 48.Obviously, any other suitable mechanism could be employed.

The air cylinder 12 has a pneumatic cylinder 50 which is provided withpressurized air to raise the bevel gear, as discussed below. Thepneumatic cylinder 50 has a rod 52 extending therefrom towards the bevelgear 28. The upper end of the rod connects to a cylinder 54 which has aforce applicator 56 mounted thereon. The force applicator 56 preferablyis firmly attached to the cylinder 54, e.g., by a set screw 58. The rod52 is guided in a bushing 60 mounted in the base 16 of the apparatus,thereby ensuring accurate alignment of the entire air cylinderapparatus. The force applicator 56 has a spud 61 extending upwardlytherefrom which fits snuggly within the bevel gear 28. The upper sidesurfaces 62 of the spud 61 preferably are curved or tapered to alloweasy insertion of the spud 61 within the bevel gear 28. Since the fitbetween the spud 61 and the bevel gear 28 is snug, the bevel gear 28 isproperly positioned relative to the other elements of the differentialonce it is mounted on the spud 61. However, this snug fit also meansthat the spud 61 may stick in the bevel gear 28, so some suitable methodsuch as the set screw 58 for fixing it to the cylinder 54 isrecommended. The lower surface of the bevel gear 28 rests against theupper surface of the force applicator 56, so the cylinder 56 can pressthe bevel gear 28 upwards towards the pinion gears 30.

The micrometer 14 has a bar 64 which is pivotally mounted to the base 16by a pivot 66. One end 68 of the bar 64 extends into an opening 70 inthe cylinder 54 of the air cylinder 12, so that it will be moved up anddown with the cylinder 54. The bar end 68 preferably is formed in theshape of a ball to minimize friction between its outer surface and theinner surface of the bore 70. A weight extension 72 preferably ismounted to the other end 74 of the bar 64. The exact position of theweight 72 relative to the bar 64 preferably is adjustable, e.g., bythreads 76, to allow for precise balancing of the bar 64. A measuringpiston 78 with an attached dial indicator 80 is mounted to the base 16by a stand 82, so that the piston 78 and dial indicator 80 are preciselypositioned relative to the base. The dial indicator 80 preferably isadjustable, e.g., by an adjustment knob 84, so that it can easily berecalibrated to zero after every use. As shown, the piston 78 pressesagainst the upper surface of the bar 64, and the dial indicator 80indicates the amount of displacement of the bar 64 at that point.Preferably, the piston 78 presses against the bar 64 at precisely thesame distance from the pivot point that the center line of the aircylinder 12 and the ball end 70 of the bar 64 are from the pivot point66. In this way, the displacement at the distance 78 is precisely thesame as the displacement at the bevel gear 28. The dial indicator 80should be marked appropriately to allow reading of the exactdisplacement. If desired, the gradations marked on the dial indicator 80could already be adjusted for the desired backlash, so that theyindicate directly the size shim to be used. The dial indicator 80 alsocould be provided with several such pre-set gradations to allow for theuse of the same apparatus with several differentials.

OPERATION

To use the apparatus just described according to the method of thepresent invention, the differential housing half 22 is first positionedon the locator ring 18. The clutch pack 26 and bevel gear 28 then arepositioned within the housing half 22. The pinion gears 30 are mountedto the corresponding cross pins 32, which then are placed in thedepressions 34 in the housing half 22. The clamp 10 then is positionedover the thus assembled differential half and closed, with the tangs 40extending between the cross pins 32 to engage the bevel gear 28. Closingof the clamp holds the cross pins 32 in the depressions 34 andcompresses the cluch pack 26 and bevel gear 28.

The air cylinder 12 then is activated to press the bevel gear 28 towardthe pinion gears 30, and released to allow the bevel gear 28 to movedownwards (aided by the spring 46). This process is repeated severaltimes to assure proper seating of the bevel gear 28 and pinion gears 30.The dial indicator 80 then is zeroed, the air cylinder 12 activated, anda reading of the distance traveled by the bevel gear 28 taken from thedial indicator 80. The pre-calculated correct displacement is subtractedfrom the reading to provide an appropriate shim pack thickness. Forexample, if the design specification calls for the displacement to be1.8 mm, while the measured displacement is 10 mm, a shim pack will bemade up of about 8.2 mm in thickness.

The clamp 10 then is released, the parts removed from the differentialhousing half 22, the shim pack 36 added, and the other parts returned tothe differential housing half 22. The clamp 10 then is closed and themeasurement process repeated. If the dial indicator 80 then is withinthe tolerance range prescribed for the backlash, the adjustment for thisdifferential half is complete. For example, with a 1.8 mm preferreddisplacement, a typical tolerance range might be anywhere between 1.0 mmand 2.3 mm displacement, so that if the dial indicator 80 is within thisrange, the backlash is considered properly adjusted. If the measurementis not within the tolerance, the difference is determined, and theappropriate thickness added to or substracted from the shim pack 36.

This process then is repeated with the other bevel gear and the otherhalf of the differential. Once the appropriate shim pack thickness isdetermined for each side of the differential, the differential canquickly be assembled and adjustment is complete.

The apparatus according to the present invention is readily adaptablefor use with a number of differently sized differentials. All that isrequired is substitution of the appropriately sized locator ring 18,force applicator 56 and adjustment of the position of the weight 72 tocounteract any differences in mass due to the different force applicator56. Of course, for sufficiently different differentials, it may benecessary to change the clamp cup 38 and tangs 40 to match the differentsizes.

It is to be understood that while the method according to the presentinvention has been described with reference to a particular apparatusfor carrying out the method, the method could be carried out using anyother suitable apparatus, or even by hand. Similarly, while the methodand apparatus have been described in connection with adjusting thebacklash in a limited slip differential, the backlash could be adjustedin a similar fashion for other types of bevel-type differentials.

While the invention has been described in conjunction with a specificembodiment, it is to be understood that many alternatives, modificationsand variations will be apparent to those skilled in the art in light ofthe aforegoing description. Accordingly, this invention is intended toembrace all such alternatives, modifications and variations which fallwithin the spirit and scope of the appended claims.

We claim:
 1. An apparatus for adjusting the backlash between the bevelgears and pinion gears of a bevel-type differential having:at least onedifferential housing half; at least one bevel gear rotatably mounted insaid housing half; and a plurality of pinion gears rotatably mountablein said housing half meshing with said bevel gear; the apparatuscomprising: means for holding the pinion gears in the differentialhousing half while allowing the pinion gears to rotate; means forselectively pressing the bevel gear along its axis of rotation in saidhousing half towards the pinion gears; and means for measuring theextent of displacement of said bevel gear when it is pressed towardssaid pinion gears.
 2. The apparatus of claim 1, further comprising meansfor pressing said bevel gear away from said pinion gears.
 3. Theapparatus of claim 1, further comprising means for precisely locatingthe differential housing relative to the means for pressing the bevelgear.
 4. An apparatus for adjusting the backlash between the piniongears and a bevel gear of a differential, comprising:a base; a clampmounted to said base for selectively holding the pinion gears into ahousing half of the differential; an air cylinder having an extensionengageable with the bevel gear and capable of pressing the bevel gearalong its axis towards the pinion gears; a locator ring mounted to saidbase for precisely positioning the differential housing half relative tosaid air cylinder; and a micrometer for measuring the displacement ofthe bevel gear upon movement thereof by the air cylinder.
 5. Theapparatus of claim 4, wherein said clamp further comprises tangsextending into contact with the bevel gear and a spring biasing saidtangs towards said bevel gear so as to press said bevel gear away fromsaid pinion gears.
 6. The apparatus of claim 4, wherein said micrometercomprises:a bar pivotally mounted to said base and having one endthereof pivotally connected to said air cylinder extension so as to bemovable with said bevel gear; a measuring piston pressing against saidbar; and a dial indicator controlled by said measuring piston.
 7. Theapparatus of claim 6, futher comprising a balance weight connected tothe end of said bar of said micrometer opposite the end attached to saidair cylinder.
 8. The application of claim 6, wherein said measuringpiston presses against said bar at a point the same distance from theopposite side of the pivot point as the distance from the pivotalconnection of the bar to the air cylinder.
 9. The apparatus of calim 8,wherein the end of said bar pivotally connected to said air cylinder isconnected to said air cylinder at a point coaxial with the air cylinder.10. An apparatus for adjusting the backlash between the pinion gears anda bevel gear of a differential, comprising:a base; a clamp mounted tosaid base for selectively holding the pinion gears into a housing halfof the differential; an air cylinder having an extension engageable withthe bevel gear and capable of pressing the bevel gear towards the piniongears; a spud on the end of said air cylinder extension for firmlyengaging said bevel gear to accurately position said bevel gear relativeto said air cylinder; and a micrometer for measuring the displacement ofthe bevel gear upon movement thereof by the air cylinder.